The long term goal of this research is to determine the mechanisms involved in the maintenance of corneal transparency and to obtain information which may offer a basis for the control and treatment of corneal diseases, some of which produce blindness. We plan to continue our work on the frog cornea with an in vitro chambered technique and an intact globe technique to determine the basic mechanisms of ion transport and the role of these mechanisms in the maintenance of corneal-fluid balance. In recent years much work has been done on the corneal epithelium and other tissues which actively transport C1-. In some of these tissues evidence indicates that active C1- transport is secondary to active Na+ and K+ transport. Theories have been formulated in attempts to explain the mechanisms by which the corneal epithelium controls the transparency of the cornea by transport of NaC1 from the stroma to the tear side. These theories will be analyzed and the analysis forms the basis for our experimental approach. An important thrust in our proposed experiments involves the effect of changes in the ionic composition of the bathing fluid on the potential difference and resistance of the epithelium and a determination of unilateral and net ionic fluxes in the open-circuited cornea. We have proposed a new theory, a pump-leak theory, for the mechanism by which the endothelium controls the transparency of the cornea and we plan to test this theory. This aspect of the work involves attempts to determine the potential difference under various conditions across the plasma membrane of the endothelial cells.